1. Field of Invention
The present invention relates to an electric converter. More particularly, the present invention relates to a DC-AC converter.
2. Description of the Prior Art
A structure of DC-AC converter of the conventional art applicable to the situation with input voltage in large range is illustrated in FIG. 1, wherein the DC-AC converter 100 includes a stage-1 voltage boost circuit 102, a stage-2 DC-DC converter 104 and a stage-3 DC-AC converter 106.
Therein, the stage-1 voltage boost circuit 102 is comprised by a DC input power 108, an inductor 110, a transistor switch 112, a diode 114 and a capacitor 116. The stage-1 voltage boost circuit 102 boosts its voltage to a level required by output end by means of pulse width modulation (PWM) operation of the transistor switch 112, and has effect to keep voltage stabilized.
The stage-2 DC-DC converter 104 is connected to an output end of the stage-1 voltage boost circuit 102 and comprises a primary control circuit 152, a voltage transformer 126 and a secondary control circuit 154.
And, the stage-2 DC-DC converter 104 receives a DC power voltage boosted by the stage-1 voltage boost circuit 102, and then delivers the output voltage from the stage-1 voltage boost circuit 102 to the primary winding of the voltage transformer 126 by means of ON/OFF operations of transistor switches 118, 120, 122 and 124 in the primary control circuit 152. Further, the voltage transformer 126 delivers the received voltage to a rectifier formed by diodes 128, 130, 132 and 134. The received voltage is also transmitted to a filter formed by a first inductor 136 and a first capacitor 138, wherefrom the output is sent to the stage-3 DC-AC converter 106.
The following stage-3 DC-AC converter 106 is coupled with the output end of the stage-2 DC-DC converter 104, comprising transistor switches 140, 142, 144, 146, an inductor 148 and a capacitor 150, and converts the received DC power voltage to AC power voltage forwarding to a load terminal by means of switching operations of transistor switch 140, 142, 144 and 146, and also by a second the filter. The second filter includes a second inductor 148 and a second capacitor 150. In the application of a conventionally known DC-AC converter with its input voltage in a large range, the input DC power voltage must be boosted to its maximum extent by the stage-1 voltage boost circuit and kept stabilized. Thereafter it is transmitted by the voltage transformer to the stage-3 DC-AC converter, wherein the DC power voltage is converted to an AC power voltage needed by the load terminal.
In summary, there are the following shortages for the conventional DC-AC converter in application for a situation with the input voltage in the large range:
1. No matter how the AC power voltage is high or low required by an output end, the DC input power voltage in stage-1 voltage boost circuit must be boosted to its highest voltage. Consequently, the components thereof must be operated or switched in the condition with a high voltage, resulting in energy consumption.
2. The converting structures of three stages are required in it, which causes an increasing energy loss and reduces a converting efficiency.
3. And two sets of heavy reservoir capacitors are employed for its configuration, leading to an increase of cost which doesn't meet economically saving consideration.